An automatic manual transmission (commonly called “AMT”) having a twin-clutch gearbox comprises a pair of primary shafts coaxial to each other, independent and fitted within each other; two coaxial clutches, each of which is adapted to connect a corresponding primary shaft to a drive shaft of a internal combustion thermal engine; and at least one secondary shaft which transmits the motion to the driving wheels and may be coupled to the primary shafts by means of corresponding pairs of clusters, each of which defines a gear.
During a gear shifting, the current gear couples the secondary shaft to a primary shaft while the successive gear couples the secondary shaft to the other primary shaft; consequently, the gear shifting occurs by crossing the two clutches, i.e., by opening the clutch associated with the current gear and simultaneously closing the clutch associated with the successive gear.
The clutches used in a twin-clutch gearbox are usually in an oil bath and are therefore operated under pressure (i.e., the degree of opening/closure of the clutch is determined by the oil pressure within the clutch itself). When a transmission control unit receives the command of gear shifting from the driver (the driver typically acts on a lever or button arranged on the steering wheel or in proximity of the steering wheel), the transmission control unit immediately starts closing the clutch associated with the successive gear; however, before the clutch associated with the successive gear may start transmitting a torque to the driving wheels, it is necessary to wait for a certain delay time interval (typically between 100 and 250 milliseconds) during which the filling of oil within the clutch is completed.
When the clutch associated with the successive gear starts transmitting a torque to the driving wheels (therefore at the end of the delay time interval) the clutch associated with the current gear is gradually opened by determining a crossing between the two clutches; it is worth noting that the opening of the clutch associated with the current gear occurs with no delay, as the clutch is already filled with oil under pressure and must be emptied of the existing oil. As the clutch associated with the successive gear increases the torque transmitted to the driving wheels, the clutch associated with the current gear complementary decreases the torque transmitted to the driving wheels so as to always keep both the torque generated by the combustion engine and the torque transmitted to the driving wheels constant.
It has been noted that the driver feels the presence of the delay (equal to the delay time interval) between the moment in which he/she generates the command of gear shifting and the moment in which he/she actually starts the gear shifting (i.e., the moment in which the clutch associated with the successive gear starts transmitting a torque to the driving wheels). Such delay, although being very limited and however not affecting the performance as the transmission of the torque to the driving wheels is never interrupted or decreased, is considered as annoying and detrimental by a substantial percentage of the drivers who wrongly believe that the traditional automatic manual transmission having a single clutch gearbox is quicker and therefore more high-performance.
Moreover, the average driver is used to the perceptions transmitted by a traditional single clutch gearbox and therefore expects to feel a “torque gap” (i.e., an “acceleration gap”) during a forward gear shifting followed by an increase in engine torque (i.e., acceleration) at the end of the forward gear shifting. On the contrary, in a standard gear shifting of a twin-clutch gearbox, during a forward gear shifting there is only felt a gradual reduction of longitudinal acceleration α of vehicle 1 by effect of the gradual lengthening of the gear ratio of the engine torque generated by engine 4; such gear shifting mode is very positive in terms of performance, but makes the majority of drivers feel exactly the opposite, i.e., is considered as detrimental to the performance.
It is worth noting that the opinion expressed by the drivers must be taken into major account even when it is technically wrong, as the vast majority of the drivers buy cars according to their own perceptions and beliefs and not based on objective criteria. In other words, what matters most is not that the vehicle has actually high performance, rather the vehicle must be felt by the drivers as having high performance.